Build off self-test (Bost) testing method

ABSTRACT

A large scale integrated circuit for a build off self-test and a device to be tested are mounted in a single socket so that their respective electrodes are in direct contact.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a build off self-test (BOST) testingmethod. More particularly, the invention relates to a method forperforming tests at high speeds with high precision, and to a socket anda semiconductor device for use with that method.

2. Description of the Background Art

One way to facilitate device testing procedures has been knownconventionally as BOST (Build Off Self Test). The BOST involves mountingon a test board an LSI or circuits for expediting examinations of adevice under test (called the DUT hereunder, including an LSI or thelike to be tested in bare-chip or packaged form). As such, the BOST isdesigned to carry out tests on high-performance multi-function DUTs byuse of an unsophisticated low-performance tester.

In a typical testing setup, a high-frequency oscillator is mounted onthe test board so that a clock signal generated thereby is used toperform tests on a DUT at frequencies higher than the tester frequency.In another setup, an operation amplifier is mounted on the test board soas to test analog signals.

FIG. 14 is a schematic view of a setup in which to practice aconventional BOST method. Referring to FIG. 14, an LSI 1008 for use withthe BOST (LSI or the like under test in bare-chip or packaged form,called the BOST LSI hereunder) receives a simple control signal from atester 1001. In turn, the BOST LSI 1008 generates test signals necessaryfor testing a DUT 1007, checks to see if output signals from the DUT1007 are correct, and notifies the tester 1001 of the results of thetests on the DUT 1007.

The BOST LSI 1008 and DUT 1007 are mounted on different sockets 1012attached to a test board 1003 and exchange relevant signals throughprinted wiring 1010. The BOST LSI 1008 and DUT 1007 use paths indicatedby broken lines in the printed wiring 1010 in order to receive from thetester 1001 the power necessary for their operations. The tester 1001thus causes the BOST LSI 1008 to operate.

Furthermore, the DUT 1007 uses the printed wiring 1010 indicated bysolid lines to exchanges signals with the BOST LSI 1008 for testing.

Part of the signals input and output to and from the DUT 1007 may beexchanged directly with the tester 1001. This arrangement is intended toalleviate loads on the BOST LSI 1008.

In the conventional BOST setup outlined above, the BOST LSI 1008 and DUT1007 are mounted on different sockets 1012 and exchange signalstherebetween via the printed wiring 1010. This has led to problems suchas a mismatch of impedance due to contactors 1006 of the differentsockets 1012, or signal delays over the printed wiring 1010.

SUMMARY OF THE INVENTION

The present invention has been conceived to solve the previouslymentioned problems, and general a object of the present invention are toprovide a novel and useful testing method, a socket for use with themethod, and a semiconductor device for use with the method.

The above object of the present invention is achieved by a testingmethod for use with a BOST setup. In the method, there are mounted on asingle socket a BOST semiconductor device and a semiconductor deviceunder test. The semiconductor device under test is tested using the BOSTsemiconductor device.

The above object of the present invention is also achieved by a socketfor use in a BOST setup. The socket includes a socket body with a spaceto accommodate a first semiconductor device. A first cap with a space toaccommodate a second semiconductor device is provided so as to pushelectrodes of the first semiconductor against contactors. A second cappushing electrodes of the second semiconductor device against theelectrodes of the first semiconductor device is also provided.

The above object of the present invention is further achieved by asemiconductor device for use in a BOST setup described below. Thesemiconductor device includes a BGA structure having conductive elasticelements attached to electrodes instead of solder balls.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a setup in which to practice a BOST methodas a first embodiment of this invention;

FIG. 2 is a schematic view of a setup in which to practice a BOST methodas a second embodiment of the invention;

FIG. 3 is a schematic view of an intermediate board for use with thesecond embodiment;

FIG. 4 is a schematic view of a socket practiced as a third embodimentof the invention;

FIG. 5 is a schematic view of a package practiced as a fourth embodimentof the invention;

FIG. 6 is a schematic view of a package practiced as a fifth embodimentof the invention;

FIG. 7 is a schematic view of a package practiced as a sixth embodimentthe invention;

FIGS. 8 to 10 are schematic views of electrode portions each practicedas a seventh embodiment of the invention;

FIG. 11 is a schematic view of a package practiced as an eighthembodiment of the invention;

FIG. 12 is a schematic view of a package practiced as a ninth embodimentof the invention;

FIG. 13 is a schematic view of a setup in which to practice a BOSTmethod in connection with the ninth embodiment; and

FIG. 14 is a schematic view of a setup in which to practice aconventional BOST method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Preferred embodiments of this invention are described below. FIG. 1 is aschematic view of a setup in which to practice a BOST method as thefirst embodiment of the invention. Referring to FIG. 1, a BOST LSI 8 anda DUT 7 are mounted on a single socket 12. This setup brings electrodesof the BOST LSI 8 and DUT 7 into direct contact with one another fortesting.

Signals of a tester 1 are input to the BOST LSI 8 via POGO pins 2 of thetester 1, printed wiring 10 of a test board 3, and contactors 6 of thesocket 12. Because the signals are exchanged at low speeds between thetester land the BOST LSI 8, a complicated transmission lineconfiguration does not adversely affect testing.

High-speed signals for testing the DUT 7 are fed from the electrodes ofthe BOST LSI 8 directly to the electrodes of the DUT 7, so that thesesignals are not affected by the transmission line configuration. Thisallows high-speed tests to be carried out with high precision.

Although the setup of FIG. 1 is shown supplying power and signals to theDUT 7 via the BOST LSI 8, this is not limitative of the invention.Alternatively, power or part of the signals may be sent directly to theDUT 7 from the tester 1. There may be a plurality of BOST LSIs 8 (whichmay be stacked one upon another or arranged side by side).

The first embodiment described above allows high-speed tests to becarried out with high precision while being less influenced by thetransmission line configuration than before.

Second Embodiment

FIG. 2 is a schematic view of a setup in which to practice a BOST methodas the second embodiment of the invention. Referring to FIG. 2, a BOSTLSI 38, an intermediate board 30, and a DUT 37 are mounted on a singlesocket 32. Electrodes of the BOST LSI 38, intermediate board 30 and DUT37 are brought into direct contact with one another for testing.

Signals from the tester 31 are input to the BOST LSI 38 via POGO pins 20of the tester 31, printed wiring 18 of a test board 33, contactors 36 ofthe socket 32, and intermediate board 30. Because the signals areexchanged at low speeds between the tester 31 and the BOST LSI 38, acomplicated transmission line configuration does not adversely affecttesting.

The electrodes of the intermediate board 30 permit supply of signals(power) of the BOST LSI 38 to suitable electrodes of the DUT 37. Thisarrangement drastically reduces the length of transmission lines andthereby allows high-speed tests to be performed with high precision.

FIG. 3 is a schematic view of an intermediate board for use with thesecond embodiment. Referring to FIG. 3, the intermediate board 30 haselectrodes 27 furnished on its face and back and includes wiring 28 tointerconnect the electrodes 27. The wiring 28 is provided to ensureelectrical conduction to the electrodes of the DUT 37 as well as to theelectrodes of the BOST LSI 38.

The BOST LSI 38 is designed for general-purpose usage so as to be ableto deal with various LSIs to be tested. The intermediate board 30 isutilized to correct mismatches in electrodes, when the roles orpositions of electrodes are different between the BOST LSI 38 and DUT37.

Unlike the first embodiment, the second embodiment described aboveeliminates the need for aligning the electrodes of the BOST LSI 38 withthose of the DUT 37. This makes it possible to apply the general-purposeBOST LSI to high-speed testing.

Third Embodiment

FIG. 4 is a schematic view of a socket practiced as the third embodimentof the invention. Referring to FIG. 4, this socket is for use with themethod of the first or the second embodiment. The socket is constitutedby a socket body 52 with a space to accommodate a BOST LSI 58, and bytwo caps 53 and 55. The cap 53 with a space to accommodate a DUT 57 isused to push electrodes of the BOST LSI 58 against contactors 56. Thecap 55 is used to push the electrodes of the DUT 57 against those of theBOST LSI 58.

In this socket, the BOST LSI 58 supports the DUT 57. The socketcomponents have clearance therebetween such that when assembled, thecomponents ensure alignment between the contactors 56 and the electrodesof the BOST LSI 58, as well as between the electrodes of the DUT 57 andthose of the BOST LSI 58.

Although the BOST LSI 58 is shown positioned under the DUT 57, this isnot limitative of the invention. The BOST LSI 58 may be placedalternatively on top of the DUT 57. Whereas the contactors 56 are shownconnected only to the electrodes of the BOST LSI 58, they may also beconnected alternatively to the electrodes of the DUT 57.

The third embodiment described above brings the BOST LSI and DUT intosecure contact with each other over the shortest possible distance.

Fourth Embodiment

FIG. 5 is a schematic view of a package practiced as the fourthembodiment of the invention. This package is based on what is known asthe ball grid array (BGA). The BGA uses solder balls in place of pins ofthe conventional pin grid array. Referring to FIG. 5, the packagecomprises: electrodes 79 of the BGA furnished on principal planes on theface and back of a package body 76; conductive rubber elements 78connected to the electrodes 79 in place of solder balls to be integratedwith the electrodes of BGA; and elastic bodies 77 (elements of suchmaterial as elastic rubber or sponge that is electrically insulating andelastic in nature) provided in parallel with the package body 76 onportions of the principal planes not covered by the conductive rubberelements 78.

The package body 76 includes wiring and an opening in which toaccommodate an LSI. The body 76 and an LSI housed in its opening make upa package. Because the electrode planes of the package comprise theconductive rubber elements 78 and elastic bodies 77, varying heights ofthe electrodes are absorbed by elasticity of the conductive rubberelements 78 or elastic bodies 77 under pressure of the socket caps. Thisarrangement eliminates faulty contact between the contactors andpackages electrodes, or between the package electrodes.

Fifth Embodiment

FIG. 6 is a schematic view of a package practiced as the fifthembodiment of the invention. Referring to FIG. 6, this package is avariation of the fourth embodiment, in which variation conductive plates83 made of metal or like material are attached to edges of theconductive rubber elements. Because the conductive rubber elements 88are not in direct contact with the contactors or with the packageelectrodes, the conductive rubber elements 88 do not wear.

In addition, with the contact planes of the package structure alsocomprising rubber elements, varying heights of the electrodes areabsorbed due to elasticity of the conductive rubber elements 88 orelastic bodies 87.

Sixth Embodiment

FIG. 7 is a schematic view of a package practiced as the sixthembodiment of the invention. Referring to FIG. 7, this package is avariation of the fifth embodiment, in which variation the conductiveplates are replaced by conductors 103 made of metal or like materialwith projections.

As with the fifth embodiment, the sixth embodiment protects conductiverubber elements 108 from wear. Because the projections scratch surfacesof the contactors or package electrodes, any metal oxide film that maydevelop over these surfaces will not impair stable contact between therelevant parts.

Seventh Embodiment

FIG. 8 is a schematic view of an electrode portion practiced as theseventh embodiment of the invention. Referring to FIG. 8, conductiverubber elements 118 instead of solder balls are attached to theelectrodes of a BGA for use with a BOST method. This arrangement causesthe conductive rubber elements 118 to absorb varying heights of thepackage electrodes and thereby ensures more stable contact between therelevant parts.

FIG. 9 is a schematic view of another electrode portion in the seventhembodiment. Referring to FIG. 9, spring-like metal elements 117 insteadof solder balls are attached to the electrodes of the BGA for use withthe BOST method. This arrangement causes the metal elements 117 toabsorb varying heights of the package electrodes and thus ensures morestable contact between the relevant parts.

FIG. 10 is a schematic view of another electrode portion in the seventhembodiment. Referring to FIG. 10, U-shaped metal elements 127 instead ofsolder balls are attached to the electrodes of the BGA for use with theBOST method. This arrangement causes the metal elements 127, in asimpler shape than the element of FIG. 9, to absorb varying heights ofthe package electrodes and thereby ensures more stable contact betweenthe relevant parts.

In describing the seventh embodiment above, the electrodes of the BGAwere shown concave-shaped. Alternatively, the electrodes may be flat inshape.

Eighth Embodiment

FIG. 11 is a schematic view of a package practiced as the eighthembodiment of the invention. Referring to FIG. 11, one of its top andbottom principal planes of this package has a structure as that of thefourth embodiment, whereas a lead frame 135 is provided to the otherplane. That is, either the top or the bottom principal plane of thepackage comprises conductive rubber elements connected to BGA electrodesas well as the conductive rubber replacing solder balls integral withthe electrodes, while the other principal plane comprises the lead frame135.

The BOST LSI generally needs, on its surface to be in contact with aDUT, approximately the same number of electrodes as those of the DUT.This makes the contact surface suitable for the BGA structure. On theother hand, the LSI surface to be in contact with a tester has fewerelectrodes. It is the reason why the tester side of the package isprovided with the lead frame 135.

In the eighth embodiment, the spring property of the lead frame on thetester side of the package helps absorb more pronounced heightdifferences than before.

Ninth Embodiment

FIG. 12 is a schematic view of a package practiced as the ninthembodiment of the invention. Referring to FIG. 12, this packagecomprises, on one of its top and bottom principal planes, staggers 156in parallel with the package surface. Other details of the structure arethe same as those of the package practiced as the fourth embodiment.

FIG. 13 is a schematic view of a setup in which to practice a BOSTmethod in connection with the ninth embodiment. Referring to FIG. 13,this is a socket constituted by a socket body 172 with a space toaccommodate a package 178, and by two caps 173 and 175. The cap 173 witha space to accommodate a DUT 177 is used to push electrodes of thepackage 178 against contactors 176. The cap 175 is used to push theelectrodes of the DUT 177 against those of the package 178. In thissocket, the DUT 177 is supported by the package 178.

The package 178 has staggers facing the DUT 177. The cap 173 has convexportions that are pushed against the staggers of the package 178 whichin turn is pressed against the contactors 176.

In the ninth embodiment, any package smaller than the DUT can be securedby the caps. This ensures stable contact between the contactors 176 onthe one hand and the electrodes of the package 178 on the other hand.

The major benefits of the present invention described above aresummarized as follows:

According to one aspect of the invention, there is provided as describeda testing method for use with a BOST setup, comprising the step ofmounting a BOST semiconductor device and a semiconductor device undertest on a single socket. This method makes it possible to carry outhigh-speed tests with high precision while being less influenced by thetransmission line configuration than before.

According to another aspect of the invention, there is provided asdescribed a testing method for use with a BOST setup, comprising thestep of mounting a BOST semiconductor device, an intermediate board, anda semiconductor device under test on a single socket so as to ensuredirect contact between electrodes of the BOST semiconductor device andthose of the intermediate board, as well as between electrodes of thesemiconductor device under test and those of the intermediate board fortesting. This method eliminates the need for aligning the electrodes ofthe BOST semiconductor device with those of the semiconductor deviceunder test and thus allows the general-purpose BOST semiconductor deviceto be applied to high-speed testing.

According to a further aspect of the invention, there is provided asdescribed a socket for use in a BOST setup, the socket comprising: asocket body with a space to accommodate a first semiconductor device; afirst cap with a space to accommodate a second semiconductor device, thefirst cap being used to push electrodes of the first semiconductoragainst contactors; and a second cap used to push electrodes of thesecond semiconductor device against the electrodes of the firstsemiconductor device. The inventive socket ensures reliable contactbetween the first and the second semiconductor devises with connectionsover the shortest possible distance.

In one preferred variation of the socket of the invention, the first capmay comprise convex portions for pushing the electrodes of the firstsemiconductor device against the contactors. This structure allows thefirst semiconductor device, smaller in size than the secondsemiconductor device, to be securely fixed by the cap and therebyensures stable contact between the contactors and the electrodes of thefirst semiconductor device.

According to a yet further aspect of the invention, there is provided asdescribed a semiconductor device for use in a BOST setup, thesemiconductor device comprising a BGA structure having conductive rubberelements attached to electrodes, the conductive rubber elementsreplacing solder balls characteristic of the BGA structure. Theinventive device ensures stable contact between the relevant parts bygetting the conductive rubber elements to absorb height differences ofthe package electrodes.

According to another aspect of the invention, there is provided asdescribed a semiconductor device for use in a BOST setup, thesemiconductor device comprising a BGA structure having spring-like metalelements attached to electrodes, the spring-like metal elementsreplacing solder balls characteristic of the BGA structure. Theinventive devices also ensures stable contact between the relevant partsby getting the spring-like metal elements to absorb height differencesof the package electrodes.

According to an even further aspect of the invention, there is providedas described a semiconductor device for use in a BOST setup, thesemiconductor device comprising: electrodes furnished on at lease one ofa top and a bottom principal planes of a body of the semiconductordevice; conductive rubber elements connected to the electrodes; andelastic bodies provided in parallel with the semiconductor device bodyon portions of the principal plane furnished with the conductive rubberelements so as not to cover the conductive rubber elements. Theinventive semiconductor device thus structured eliminates faulty contactbetween the contactors and electrodes thereof as well as betweenelectrodes of another semiconductor device and electrodes thereof byabsorbing height differences therebetween.

In a preferred variation of the semiconductor device of the invention,the semiconductor device may further comprise conductive plates attachedto edges of the conductive rubber elements. This structure protects therubber elements against wear.

In another preferred variation of the semiconductor device of theinvention, the semiconductor device may further comprise projectionsattached to edges of the conductive rubber elements. This structureprevents the wear of the conductive rubber elements and, with theprojections scratching surfaces of the contactors or electrodes ofanother semiconductor device, prevents any metal oxide film that maydevelop on such surfaces from impairing stable contact between therelevant parts.

In a further preferred variation of the semiconductor device of theinvention, one of the top and bottom principal planes of thesemiconductor device body may comprise staggers in parallel with thesemiconductor device body. This structure allows to perform asemiconductor test even when the semiconductor device is smaller thanthe semiconductor device under test and to be placed under the same.

According to a still further aspect of the invention, there is providedas described a semiconductor device for use in a BOST setup, thesemiconductor device comprising: electrodes furnished on one of a topand a bottom principal plane of a body of the semiconductor device;conductive rubber elements connected to the electrodes; elastic bodiesprovided in parallel with the semiconductor device body on portions ofthe principal plane so as not to cover the conductive rubber elements;and a lead frame furnished on the other principal plane of thesemiconductor device body. The inventive device helps absorb morepronounced height differences than before between the contact surfaces.

Further, the present invention is not limited to these embodiments, butvariations and modifications may be made without departing from thescope of the present invention.

The entire disclosure of Japanese Patent Application No. Hei 11-373241filed on Dec. 28, 1999 including specification, claims, drawings andsummary are incorporated herein by reference in its entirety.

What is claimed is:
 1. A testing method for a build off self-test (BOST)setup, comprising: mounting a BOST semiconductor device and asemiconductor device under test in a single socket; and testing thesemiconductor device under test using the BOST semiconductor device. 2.The testing method according to claim 1, further comprising mounting anintermediate board on the single socket together with the BOSTsemiconductor device and the semiconductor device under test to ensuredirect contact between electrodes of the BOST semiconductor device andthe electrodes of the intermediate board, as well as between electrodesof the semiconductor device under test and electrodes of theintermediate board for testing.
 3. The testing method according to claim1, including placing respective electrodes of the BOST semiconductordevice and the semiconductor device under test in direct contact witheach other in the single socket for testing.